UV Radiation Effects on Plant Growth and Forage Quality in a Shortgrass Steppe Ecosystem

Authors

  • Daniel G. Milchunas,

    Corresponding author
    1. Forest, Range, and Watershed Stewardship Department, Colorado State University, Fort Collins, CO
    2. Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO
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  • Jennifer Y. King,

    1. Department of Soil, Water, and Climate, and Department of Ecology, Evolution, and Behavior, University of Minnesota, St. Paul, MN
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  • Arvin R. Mosier,

    1. Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO
    2. USDA-ARS Soil Plant Nutrient Research Unit, Fort Collins, CO
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  • John C. Moore,

    1. Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO
    2. Department of Biological Sciences, University of Northern Colorado, Greeley, CO
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  • Jack A. Morgan,

    1. USDA-ARS Rangeland Resources Research Unit, Crops Research Laboratory, Fort Collins, CO
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  • Meghan H. Quirk,

    1. Department of Biological Sciences, University of Northern Colorado, Greeley, CO
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  • James R. Slusser

    1. Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO
    2. USDA UV-B Monitoring and Research Program, Colorado State University, Fort Collins, CO
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  • Posted on the website on 28 February 2004

*To whom correspondence should be addressed: Forest, Range and Watershed Stewardship Department. Colorado State University, Fort Collins, CO 80523, USA, Fax: 970-491-2156: e-mail: daniel.milchunas@colostate.edu

ABSTRACT

Levels of UV were manipulated in a native shortgrass steppe using open-sided structures with tops that either passed or blocked wavelengths shorter than ∼370 nm. Precipitation was controlled to create a drought or a very wet year. Subplots were either nondefoliated or defoliated to simulate grazing by livestock, which is the primary land use. Plant community productivity and forage quality were assessed in response to the two climate change variables (UV, precipitation) and grazing stress. Productivity and seasonal standing biomass of the dominant grass species were negatively affected by passing versus blocking UV, but only in the dry year. Another species was negatively affected by passing UV in the wet year, indicating the potential for future shifts in species composition. Forage quality for ruminants increased when UV was passed compared with blocked, as determined by in vitro digestible dry matter, depending on species and precipitation. Nitrogen concentrations and soluble and fiber components of vegetation also displayed some UV effects, but they were generally small and depended on species, season or amount of precipitation (or all). Grazing treatment had large positive effects on current-year productivity only in the wet year and some small positive effects on quality in both wet and dry years. Interactions between UV and grazing treatment were not observed.

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